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Subject[PATCH v2 2/5] mm: Extends local cpu counter vm_diff_nodestat from s8 to s16
Date
The type s8 used for vm_diff_nodestat[] as local cpu counters has the
limitation of global counters update frequency, especially for those
monotone increasing type of counters like NUMA counters with more and more
cpus/nodes. This patch extends the type of vm_diff_nodestat from s8 to s16
without any functionality change.

before after
sizeof(struct per_cpu_nodestat) 28 68

Signed-off-by: Kemi Wang <kemi.wang@intel.com>
---
include/linux/mmzone.h | 4 ++--
mm/vmstat.c | 16 ++++++++--------
2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index c06d880..2da6b6f 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -289,8 +289,8 @@ struct per_cpu_pageset {
};

struct per_cpu_nodestat {
- s8 stat_threshold;
- s8 vm_node_stat_diff[NR_VM_NODE_STAT_ITEMS];
+ s16 stat_threshold;
+ s16 vm_node_stat_diff[NR_VM_NODE_STAT_ITEMS];
};

#endif /* !__GENERATING_BOUNDS.H */
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 1dd12ae..9c681cc 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -332,7 +332,7 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
long delta)
{
struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
- s8 __percpu *p = pcp->vm_node_stat_diff + item;
+ s16 __percpu *p = pcp->vm_node_stat_diff + item;
long x;
long t;

@@ -390,13 +390,13 @@ void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
{
struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
- s8 __percpu *p = pcp->vm_node_stat_diff + item;
- s8 v, t;
+ s16 __percpu *p = pcp->vm_node_stat_diff + item;
+ s16 v, t;

v = __this_cpu_inc_return(*p);
t = __this_cpu_read(pcp->stat_threshold);
if (unlikely(v > t)) {
- s8 overstep = t >> 1;
+ s16 overstep = t >> 1;

node_page_state_add(v + overstep, pgdat, item);
__this_cpu_write(*p, -overstep);
@@ -434,13 +434,13 @@ void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
{
struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
- s8 __percpu *p = pcp->vm_node_stat_diff + item;
- s8 v, t;
+ s16 __percpu *p = pcp->vm_node_stat_diff + item;
+ s16 v, t;

v = __this_cpu_dec_return(*p);
t = __this_cpu_read(pcp->stat_threshold);
if (unlikely(v < - t)) {
- s8 overstep = t >> 1;
+ s16 overstep = t >> 1;

node_page_state_add(v - overstep, pgdat, item);
__this_cpu_write(*p, overstep);
@@ -533,7 +533,7 @@ static inline void mod_node_state(struct pglist_data *pgdat,
enum node_stat_item item, int delta, int overstep_mode)
{
struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
- s8 __percpu *p = pcp->vm_node_stat_diff + item;
+ s16 __percpu *p = pcp->vm_node_stat_diff + item;
long o, n, t, z;

do {
--
2.7.4
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